This invention relates generally to electronically controlled fuel injected engines and, more particularly, to controlling fuel injection signals during engine acceleration or deceleration wherein at least one of the fuel injection shots associated with a multi-shot fuel injection event may be disabled to control fuel emissions.
Electronically controlled fuel injectors are well known in the art including both hydraulically actuated electronically controlled fuel injectors as well as mechanically actuated electronically controlled fuel injectors. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of a fuel injection signal received from an electronic controller. These signals include waveforms that are indicative of a desired fuel injection rate as well as the desired timing and quantity of fuel to be injected into the respective cylinders of the engine.
Emission regulations pertaining to engine exhaust emissions are becoming increasingly restrictive throughout the world including, for example, restrictions on the emission of hydrocarbons, carbon monoxide, the release of particulates, and the release of oxides of nitrogen (NOx). Tailoring the fuel injection waveform, that is the number of injections and the injection rate of fuel to a combustion chamber, as well as the quantity and timing of such fuel injections, is one way to improve emissions and meet higher emissions standards. As a result, multiple fuel injection techniques, wherein the fuel injection waveform comprises a plurality of distinct fuel injection signals, have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Multiple fuel injections typically involve splitting the total fuel delivery to the cylinder during a particular injection event into separate fuel injections, such as a pilot injection, a main injection, and an anchor injection where a three shot injection is desired. Each of these injections may also be referred to generally as a shot, and the term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector indicative of an injection or delivery of fuel to the engine. At different engine operating conditions, it may be necessary to use different injection strategies in order to achieve both desired engine performance and emissions control.
As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four stroke engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine.
During certain acceleration events, not all of the fuel delivered to the engine in the distinct fuel shots of a multi-shot fuel injection event is combusted for a variety of reasons. For example, where a turbo charger is used, during an acceleration event the air mass delivered to the engine is lower because the turbo charger device associated with the engine has to spin up to deliver a greater quantity of air corresponding to the increase in the fuel. When a rich fuel mixture is introduced into the cylinder, more fuel is likely to contact the cylinder walls than with a comparatively leaner fuel mixture. Because a cylinder""s walls are typically cooler in comparison to the interior of the cylinder, the fuel does not combust but instead mixes with the cylinder wall lubricating oil. This fuel deteriorates the lubricating quality of the engine oil, and adversely impacts the fuel efficiency of the engine. Furthermore, such uncombusted fuel may be emitted in the form of hydrocarbons, which are a pollutant and therefore an undesirable component of an engine""s emissions.
Further during an acceleration event, the time duration of fuel injection events may decrease. It becomes more difficult to inject multiple shots into a shrinking time window for a cylinder as engine speed increases. Rapidly changing engine speed can cause timing errors for all shots but especially the anchor shot since it is a time delay after the main shot. As a result, the time difference between the end of one fuel shot in a particular fuel injection event and the beginning of a subsequent fuel shot in the same fuel injection event decreases. Therefore, it becomes increasingly important to deliver the individual fuel shots accurately as the timing between fuel shots becomes tighter. However, the changing engine speed corresponds to a change in the crank angle for injecting the particular fuel shot. Therefore, the desired angle determined for the injection of each fuel shot in each fuel injection event might be slightly offset from the actual desired angle of injection. Such a situation is not desirable because offset fuel injection shots may detrimentally impact the engine""s performance, efficiency, and emissions.
In a deceleration event, on the other hand, the amount of fuel delivered in a fuel injection event decreases. As the amount of fuel decreases, it becomes increasingly difficult to physically partition the fuel into distinct fuel shots. For small enough amounts of fuel, the improperly partitioned amounts of fuel may result in improper or undesirable performance, efficiency, and emissions of the engine.
Further during a deceleration event, the time duration of each fuel injection may increase. As discussed for acceleration above, the time to angle conversion for the individual fuel shots may be inaccurate when the speed of the engine is changing. As a result, the inaccurate (or offset) fuel injection events may detrimentally impact the engine""s performance, efficiency, and emissions during a deceleration event.
It is therefore desirable to provide an apparatus and method to control the delivery of fuel to an engine to control emissions during acceleration and deceleration. Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, an apparatus and method is disclosed for electronically controlling a multi-shot fuel injection event during acceleration and deceleration events to better control the engine""s fuel emissions during such events. More particularly, an electronic controller is operable to recognize an acceleration or deceleration event based upon certain sensed engine parameters and thereafter dynamically adjust the number of fuel injections to control the delivery of fuel to the engine during acceleration or deceleration events. As a result, the engine""s emissions may be maintained within predetermined limits during the acceleration and deceleration events.